1. Field of the Invention
The present invention relates to an information recording method, an information recording medium and an information recording apparatus, using a recording medium in which information can be recorded by energy beam irradiation. Particularly, it relates to an information recording method having an excellent effect on a phase-change optical disk, an information recording medium, and an information recording apparatus using the information recording method.
2. Description of the Related Art
In the case of using, for example, such a photo-magnetic disk as described in JP-A-62-175948 having a switched connection two-layer film as a recording film, or in the case of using, for example, such a high-speed erasable recording film for a phase-change optical disk as described in JP-A-62-259229 capable of performing crystallization in almost the same time as laser irradiation time for recording, a conventional recording/erasing method on a rewritable recording film is carried out by changing a power level of an energy beam between at least two power levels (that is, at least a high power level and an intermediate power level) which are higher than a read power level. The conventional method has an advantage in that new information can be recorded while existing information is erased, that is, overwriting (rewriting owing to overwriting) can be made. Further, such a phenomenon that a recording mark is shaped like a teardrop (a rear portion of a recording mark becomes wider than a front portion of the recording mark) can be suppressed by changing a power level of an energy beam among three power levels consisting of a high power level, an intermediate power level and a low power level lower than the intermediate power level as described in JP-A-62-259229 and JP-A-3-185629.
On the other hand, recently, a DVD-RAM using a phase-change material to achieve a memory capacity of 2.6 GB per side in a 120 mm-diameter disk has been put into practical use. A recording control method used in the DVD-RAM is described in JIS Standard, JIS×6243 for 120 mm DVDRwritable Disk (DVD-RAM) (hereinafter referred to as “Standard Book JIS X 6243”), page 86. Control based on the aforementioned three power levels is described in the standard book.
Researches into improvement of the density of a rewritable digital video disk (DVD-RAM) using a phase-change recording film are in progress. In an optical disk device such as a DVD-RAM in which mark edge recording is performed in a phase-change recording film, both attained temperature and cooling speed in a recording mode need to be made substantially uniform in every place of an outer edge portion of a recording-film fused region for forming recording marks in the recording film in order to prevent both mark shape distortion and incomplete erasure. However, in various types of known recording waveforms, it is impossible to satisfy the condition sufficiently. Accordingly, there is a limitation in realizable recording density. Further, recording characteristic of a recording medium usually varies according to the producer, production time and lot of the recording medium. Accordingly, there is a tendency for recording compatibility to be more hardly secured as higher-density recording is intended.
Particularly, in a DVD-RAM with a memory capacity of 4.7 GB higher in density than the DVD-RAM with a memory capacity of 2.6 GB, recording is performed with the same spot diameter as that in the 2.6 GB DVD-RAM so that the compatibility with 2.6 GB DVD-RAM can be kept easily. However, when linear density is increased while the spot diameter is kept constant, the distance between positions irradiated on a recording medium by two recording pulses adjacent to each other is reduced compared with the light spot diameter of laser light on the recording medium. Accordingly, light distributions overlap each other compared with the 2.6 GB DVD-RAM, so that it is necessary to prevent the recording mark shape from being distorted due to the overlapping of light distributions. Therefore, it is thought of that more complicated modulated recording waveform control is used to increase the number of power levels so as to change the energy beam among four power levels. In such a complicated recording waveform, good-shape recording marks can be formed if appropriate setting is performed. Increase of the number of energy levels, however, brings about a problem of how to optimize the respective energy levels. That is, when the respective energy levels are set appropriately, good recording marks having little recording mark shape distortion can be formed. But, there is a problem that the procedure of optimizing the energy levels is complicated because energy balance becomes delicate and the number of energy levels is large (first problem).
In the conventional recording/erasing method applied to the rewritable recording film as described in the aforementioned Standard Book JIS X 6243, page 86, the control on the basis of the aforementioned three power levels is described. The recording power levels used in the recording mode are written in a control data area on the disk. The information recording apparatus sets the recording power levels by reading the recording power levels written on the disk. The absolute values of the recording power levels, however, may change due to the individual difference of the information recording apparatus, or due to the environmental change or aging of the information recording apparatus. In most cases, therefore, the recording power levels are checked or adjusted before information is written in the disk actually. That is, while Peak Power is changed in a condition that Bias Power 1 and Bias Power 2 given to the control data area are fixed, a random pattern is recorded and then reproduced to measure reproductive jitter. The recording power level to make the value of reproductive jitter equal to a predetermined value is multiplied by a predetermined factor so that a recording power level is obtained. The recording power level obtained thus is set as new Peak Power. Then, while Bias Power 1 is changed, the random pattern is recorded and then reproduced to measure the reproductive jitter. The bias power to minimize the value of the reproductive jitter is set as new Bias Power 1.
In a phase-change recording medium of a 120 mm diameter with a larger capacity than 2.6 GB per side (for example, a DVD-RAM with a diameter of 120 mm intended to achieve a capacity of 4.7 GB per side), accurate information recording may be performed by adaptively changing the timing of leading and trailing edge portions of a recording pulse in accordance with the combination of recording patterns to be recorded. It is thought of that such timing information is recorded in the control data area on the disk so that the information recording apparatus reads the timing information to use it for actual recording.
The information recording apparatus does not always have the same recording characteristic. The recording characteristic may change due to the individual difference of the information recording apparatus, or due to the aging or environmental change of the information recording apparatus. Accordingly, it may be impossible to perform appropriate recording on the basis of the timing information written on the disk. In such a case, the reproductive jitter at the time of recording/reproducing the random pattern becomes worse than the expected value. As a result, if the recording power levels are determined on the basis of the jitter of the random pattern in the same manner as that in the prior art, there is a possibility that the recording power levels may be set to unsuitable values. If the recording is performed on the basis of the unsuitable recording power levels, there is a fear of reduction in reliability of recording/reproducing, for example, the recording becomes unstable, the already written information is erased due to cross-erasure, and so on (second problem).
Further, as described above, in the DVD-RAM with the recording capacity of 4.7 GB which is higher in density than the 2.6 GB DVD-RAM, the recording can be performed with the same spot diameter as that in the 2.6 GB DVD-RAM so that the compatibility with the 2.6 GB DVD-RAM can be obtained. However, when the linear density is made high while the spot diameter is kept unchanged, the distance between two positions on the recording medium irradiated with two adjacent recording pulses is reduced compared with the light spot diameter of laser light on the recording medium. For this reason, the light distributions overlap each other compared with the case of 2.6 GB, so that it is necessary to prevent the recording mark shape distortion due to the overlapping of the light distributions. Further, when the space between the recording marks is short, the recording marks cannot be resolved by the reading light spot, so that the shifting of the recording mark edge position occurs in the reproductive signal waveform. Accordingly, it is also necessary to prevent the recording mark edge position from shifting. For this reason, an attempt has been made to reduce the shifting of the recording mark edge position by changing the irradiation timing of the recording pulses according to the length of a mark to be written and the length of a portion (hereinafter referred to as “space”) between marks. However, when high-density recording is to be performed by use of the phase-change medium such as a DVD-RAM with the recording capacity of 4.7 GB, there is a problem that the procedure for determining the irradiation timing of the recording pulses in detail is not always clear (third problem).